1. Field of the Invention
The invention relates to a process for the C-monoalkylation or C-dialkylation of a dialkyl malonate with an alkyl halide or an alkylene dihalide having vicinal halogen atoms and potassium carbonate (potash) as the hydrogen halide acceptor.
2. Description of Related Art
DE 43 26 917 describes a process for the preparation of cyclopropane-1,1-dicarboxylic esters from dialkyl malonates and alkylene dihalides having vicinal halogen atoms (referred to below as alkylene dihalides for short) with potassium carbonate as a hydrogen halide acceptor and dimethylformamide or dimethylacetamide as a solvent. In the process, a) alkylene dichlorides are employed, b) potassium carbonate having fine particle fractions of 85% or more smaller than 0.1 mm and 70% or more smaller than 0.05 mm is used, c) the water of reaction is distilled off azeotropically during the reaction, d) the reaction temperature is brought to 90 to 160.degree. C. and e) the molar ratio of dialkyl malonate to alkylene dichloride to potassium carbonate is chosen as 1:(2.5-3.5):(1.0-1.4).
This process constitutes a significant improvement over previously known procedures. Thus, even the cheaply available alkylene dichlorides give yields of more than 80% of theory, which could not be achieved according to D.A. White, Synthetic Communications, 1977, page 599, even with the corresponding alkylene dibromides. Instead of potassium bromide which is difficult to dispose of, potassium chloride, which can be used for the electrolytic preparation of potassium hydroxide, is obtained. The space-time yields for reaction times of from 5 to 6 hours are considerably better than in the process of D.A. White, loc. cit., which requires 22 hours, and in the procedure according to J. Heiszman et al., Synthesis Communications 1987, page 738, in which alkylene dichlorides are employed with benzene as a solvent, a phase-transfer catalyst is used and the reaction time is 20 hours.
There is a need for a process for C-alkylating or dialkyl malonate where the process provides an enhanced conversion of dialkyl malonate relative to conventional processes.